Allah is The Most Merciful, The Forgiver. Those who repent their sins and sincerely seek forgiveness with giving back the rights of others and firm decision not to commit the sin again have been promised by Allah in Quran: Say, O My servants who have transgressed against themselves (by sinning), Despair not of the Mercy of Allah, Verily, Allah forgives all sins, Truly He is Oft-Forgiving, Most Merciful. (Sura 39, Verse 53).
The Hadeeth says: The repenting believer from his sin is like a person with out sin. التائب من الذنب كمن لا ذنب له.
Repenting and sincerely seeking forgiveness and fulfilling the missed rights have definite effect in our life and spirituality.
Wassalam.